A molded polyurethane or rubber unit sole is often used to construct women's high heel shoes. The molded unit sole forms the outer sole of the shoe and the heel may also be molded into the one piece unit. The upper of the shoe may then be glued, stitched or otherwise secured to the unit sole to provide for the economical manufacture of women's high heel shoes.
The arch and heel area of a unit sole requires bracing and strengthening because the materials used in molding the unit sole are resilient to provide proper cushioning and wear for the outer sole. In a high heeled women's shoe especially, the arch and heel area is subjected to significant pressures and forces tending to flex the shoe in both the heel to toe and the side to side directions. The amount of flex in the unit sole must be limited to avoid ankle injuries and subsequent product liability claims. In the prior art, the usual way of strengthening the unit sole is to insert a 3/16 inch square rod into the mold which extends from approximately half way into the heel and over the top of the arch for about one half the length of the elevated section of the arch. This steel insert is molded in place and does provide some limited amount of rigidity to the heel and top of the arch. However, there is no significant increase in the rigidity from heel to toe or from side to side to reduce the "flex" of the unit sole.
In addition to the "flex" problem inherent in a molded unit sole, cost plays an important part in determining the structure and materials which can be utilized. Because of the high volume production runs in manufacturing shoes, it is very important to constantly find ways to increase the quality of the shoe while reducing the unit price, if possible. A savings of a few pennies on each shoe results in significant savings as over 400 million shoes are purchased by the American shoe industry every year.
Applicant has succeeded in developing a new shank insert for supporting the heel and arch area which provides a markedly increased stability from heel to toe and side to side, extends much further through the unit sole and heel, provides an easy and convenient mounting for a top lift at the bottom of the heel, is significantly reduced in cost, and which provides other advantages as will be described. Applicant's shank support includes a steel shank plate approximately 3/4 inch wide and only about 0.065 thousandths thick which extends the full length of the elevated portion of the arch and into the heel area. A strengthening rib is stamped into the length of the steel shank to increase its resistance to twisting and flexing. Alternately, the steel shank may be oval in shape. The steel shank is easily fashioned into different shapes to fit varying styles of unit soles and its generally flattened tongue-like appearance permits it to extend all the way through the entire length of the elevated arch portion of the unit sole where the mold is relatively narrow.
A heel post and fastening member extends downwardly at the rear of the steel shank portion and through the entire height of the heel. The heel post may consist of a case hardened screw with a wing nut reversed and threaded up the heel post to contact the steel shank. The heel post may extend out the bottom of the heel and top lifts for the heel may be screwed onto the heel post and secured into position thereby. Holes may be drilled into the steel shank to aid in positioning the shank during the molding process, as is known in the art.
Applicant's steel shank support also provides a significant cost savings over the prior art device as it may be fashioned from readily available materials such as case hardened steel screws, wing nuts, and sheet steel or strapping. The prior art square rod contains more metal and is more expensive to form into a useable shape. However, very little effort is required to form applicant's steel shank into the proper curvature and it may be rapidly stamped or otherwise inexpensively processed into final form.
Applicant's steel shank support is safer and eliminates the discomfort sometimes experienced with the prior art device as it presents a generally flattened base along the upper edge of the unit sole which does not tend to work its way up towards the bottom of the foot. The 3/16 inch steel shank of the prior art is not flattened and has a tendency to work its way to the top of the molded unit sole if not properly molded or if the shoe is not otherwise properly constructed. In addition, it is well known that consumers are becoming more conscious of potential claims against manufacturers of all sorts of products, including shoes. With applicant's device, increased rigidity and stability is provided in both the heel to toe and side to side directions which significantly reduces the possibility that the ankle would be injured as a result of the shoe failing during use.
These and other advantages of applicant's device may be more fully understood by referring to the drawings and preferred embodiment which follows.